Magnetic recording medium and magnetic storage apparatus

ABSTRACT

A magnetic recording medium is provided with at least one exchange layer structure, and a magnetic layer formed on the exchange layer structure. The exchange layer structure includes a ferromagnetic layer, and a non-magnetic coupling layer provided on the ferromagnetic layer and under the magnetic layer. The ferromagnetic layer and the magnetic layer have antiparallel magnetizations.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to magnetic recordingmedia and magnetic storage apparatuses, and more particularly to amagnetic recording medium and a magnetic storage apparatus which aresuited for high-density recording.

[0003] 2. Description of the Related Art

[0004] The recording density of longitudinal magnetic recording media,such as magnetic disks, has been increased considerably, due to thereduction of medium noise and the development of magnetoresistive andhigh-sensitivity spin-valve heads. A typical magnetic recording mediumis comprised of a substrate, an underlayer, a magnetic layer, and aprotection layer which are successively stacked in this order. Theunderlayer is made of Cr or a Cr-based alloy, and the magnetic layer ismade of a Co-based alloy.

[0005] Various methods have been proposed to reduce the medium noise.For example, Okamoto et al., “Rigid Disk Medium For 5 Gbit/in²Recording”, AB-3, Intermag '96 Digest proposes decreasing the grain sizeand size distribution of the magnetic layer by reducing the magneticlayer thickness by the proper use of an underlayer made of CrMo, and aU.S. Pat. No. 5,693,426 proposes the use of an underlayer made of NiAl.Further, Hosoe et al., “Experimental Study of Thermal Decay inHigh-Density Magnetic Recording Media”, IEEE Trans. Magn. Vol.33, 1528(1997), for example, proposes the use of an underlayer made of CrTiB.The underlayers described above also promote c-axis orientation of themagnetic layer in a plane which increases the remanence magnetizationand the thermal stability of written bits. In addition, proposals havebeen made to reduce the thickness of the magnetic layer, to increase theresolution or to decrease the width of transition between written bits.Furthermore, proposals have been made to decrease the exchange couplingbetween grains by promoting more Cr segregation in the magnetic layerwhich is made of the CoCr-based alloy.

[0006] However, as the grains of the magnetic layer become smaller andmore magnetically isolated from each other, the written bits becomeunstable due to thermal activation and to demagnetizing fields whichincrease with linear density. Lu et al., “Thermal Instability at 10Gbit/in² Magnetic Recording”, IEEE Trans. Magn. Vol.30, 4230 (1994)demonstrated, by micromagnetic simulation, that exchange-decoupledgrains having a diameter of 10 nm and ratio K_(u)V/k_(B)T=60 in 400 kfcidi-bits are susceptible to significant thermal decay, where K_(u)denotes the magnetic anisotropy constant, V denotes the average magneticgrain volume, k_(B) denotes the Boltzmann constant, and T denotes thetemperature. The ratio K_(u)V/k_(B)T is also referred to as a thermalstability factor.

[0007] It has been reported in Abarra et al., “Thermal Stability ofNarrow Track Bits in a 5 Gbit/in² Medium”, IEEE Trans. Magn. Vol.33,2995 (1997) that the presence of intergranular exchange interactionstabilizes written bits, by MFM studies of annealed 200 kfci bits on a 5Gbit/in² CoCrPtTa/CrMo medium. However, more grain decoupling isessential for recording densities of 20 Gbit/in² or greater.

[0008] The obvious solution has been to increase the magnetic anisotropyof the magnetic layer. But unfortunately, the increased magneticanisotropy places a great demand on the head write field which degradesthe “overwrite” performance which is the ability to write overpreviously written data.

[0009] In addition, the coercivity of thermally unstable magneticrecording medium increases rapidly with decreasing switching time, asreported in He et al., “High Speed Switching in Magnetic RecordingMedia”, J. Magn. Magn. Mater. Vol.155, 6 (1996), for magnetic tapemedia, and in J. H. Richter, “Dynamic Coervicity Effects in Thin FilmMedia”, IEEE Trans. Magn. Vol.34, 1540 (1997), for magnetic disk media.Consequently, the adverse effects are introduced in the data rate, thatis, how fast data can be written on the magnetic layer and the amount ofhead field required to reverse the magnetic grains.

[0010] On the other hand, another proposed method of improving thethermal stability increases the orientation ratio of the magnetic layer,by appropriately texturing the substrate under the magnetic layer. Forexample, Akimoto et al., “Relationship Between Magnetic CircumferentialOrientation and Magnetic Thermal Stability”, J. Magn. Magn. Mater.(1999), in press, report through micromagnetic simulation, that theeffective ratio K_(u)V/k_(B)T is enhanced by a slight increase in theorientation ratio. This further results in a weaker time dependence forthe coercivity which improves the overwrite performance of the magneticrecording medium, as reported in Abarra et al., “The Effect ofOrientation Ratio on the Dynamic Coercivity of Media for >15 Gbit/in²Recording”, EB-02, Intermag '99, Korea.

[0011] Furthermore, keepered magnetic recording media have been proposedfor thermal stability improvement. The keeper layer is made up of amagnetically soft layer parallel to the magnetic layer. This soft layercan be disposed above or below the magnetic layer. Oftentimes, a Crisolation layer is interposed between the soft layer and the magneticlayer. The soft layer reduces the demagnetizing fields in written bitson the magnetic layer. However, coupling the magnetic layer to acontinuously-exchanged coupled soft layer defeats the purpose ofdecoupling the grains of the magnetic layer. As a result, the mediumnoise increases.

[0012] Various methods have been proposed to improve the thermalstability and to reduce the medium noise. However, there was a problemin that the proposed methods do not provide a considerable improvementof the thermal stability of written bits, thereby making it difficult togreatly reduce the medium noise. In addition, there was another problemin that some of the proposed methods introduce adverse effects on theperformance of the magnetic recording medium due to the measures takento reduce the medium noise.

[0013] More particularly, in order to obtain a thermally stableperformance of the magnetic recording medium, it is conceivable to (i)increase the magnetic anisotropy constant K_(u), (ii) decrease thetemperature T or, (iii) increase the grain volume V of themagnetic-layer. However, measure (i) increases the coercivity, therebymaking it more difficult to write information on the magnetic layer. Inaddition, measure (ii) is impractical since in magnetic disk drives, forexample, the operating temperature may become greater than 60° C.Furthermore, measure (iii) increases the medium noise as describedabove. As an alternative for measure (iii), it is conceivable toincrease the thickness of the magnetic layer, but this would lead todeterioration of the resolution.

SUMMARY OF THE INVENTION

[0014] Accordingly, it is a general object of the present invention toprovide a novel and useful magnetic recording medium and magneticstorage apparatus, in which the problems described above are eliminated.

[0015] Another and more specific object of the present invention is toprovide a magnetic recording medium and a magnetic storage apparatus,which can improve the thermal stability of written bits withoutincreasing the medium noise, so as to enable a reliable high-densityrecording without introducing adverse effects on the performance of themagnetic recording medium, that is, unnecessarily increasing themagnetic anisotropy.

[0016] Another object of the present invention is to provide a magneticrecording medium comprising at least one exchange layer structure, and amagnetic layer formed on the exchange layer structure, where theexchange layer structure comprises a ferromagnetic layer, and anon-magnetic coupling layer provided on the ferromagnetic layer andunder the magnetic layer, and the ferromagnetic layer and the magneticlayer have antiparallel magnetizations. According to the magneticrecording medium of the present invention, it is possible to provide amagnetic recording medium which can improve the thermal stability ofwritten bits, so as to enable reliable high-density recording withoutdegrading the overwrite performance.

[0017] Still another object of the present invention is to provide amagnetic storage apparatus comprising at least one magnetic recordingmedium including at least one exchange layer structure and a magneticlayer formed on said exchange layer structure, and at least one headrecording information on and/or reproducing information from therecording medium, where the exchange layer structure comprises aferromagnetic layer and a nonmagnetic coupling layer provided on theferromagnetic layer and under the magnetic layer, and the ferromagneticlayer and the magnetic layer have antiparallel magnetizations. Accordingto the magnetic storage apparatus of the present invention, it ispossible to provide a magnetic storage apparatus which can improve thethermal stability of written bits, so as to enable a reliablehigh-density recording without introducing adverse effects on theperformance of the magnetic recording medium.

[0018] Other objects and further features of the present invention willbe apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a cross sectional view showing an important part of afirst embodiment of the magnetic recording medium according to thepresent invention;

[0020]FIG. 2 is a cross sectional view showing an important part of asecond embodiment of the magnetic recording medium according to thepresent invention;

[0021]FIG. 3 is a diagram showing an in-plane magnetization curve of asingle CoPt layer having a thickness of 10 nm on a Si substrate;

[0022]FIG. 4 is a diagram showing an in-plane magnetization curve of twoCoPt layers separated by a Ru layer having a thickness of 0.8 nm;

[0023]FIG. 5 is a diagram showing an in-plane magnetization curve of twoCoPt layers separated by a Ru layer having a thickness of 1.4 nm;

[0024]FIG. 6 is a diagram showing an in-plane magnetization curve twoCoCrPt layers separated by a Ru having a thickness of 0.8 nm;

[0025]FIG. 7 is a cross sectional view showing an important part of anembodiment of the magnetic storage apparatus according to the presentinvention; and

[0026]FIG. 8 is a plan view showing the important part of the embodimentof the magnetic storage apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] A description will hereinafter be given of embodiments of thepresent invention, by referring to the drawings.

[0028] First, a description will be given of the operating principle ofthe present invention.

[0029] The present invention submits the use of layers with antiparallelmagnetization structures. For example, S. S. P. Parkin, “SystematicVariation of the Strength and Oscillation Period of Indirect MagneticExchange Coupling through the 3d, 4d, and 5d Transition Metals”, Phys.Rev. Lett. Vol.67, 3598 (1991) describes several magnetic transitionmetals such as Co, Fe and Ni that are coupled through thin non-magneticinterlayers such as Ru and Rh. On the other hand, a U.S. Pat. No.5,701,223 proposes a spin-valve which employs the above described layersas laminated pinning layers to stabilize the sensor.

[0030] For a particular Ru or Ir layer thickness between twoferromagnetic layers, the magnetizations can be made parallel orantiparallel. For example, for a structure made up of two ferromagneticlayers of different thickness with antiparallel magnetizations, theeffective grain size of a magnetic recording medium can be increasedwithout significantly affecting the resolution. A signal amplitudereproduced from such a magnetic recording medium is reduced due to theopposite magnetizations, but this can be rectified by adding anotherlayer of appropriate thickness and magnetization direction, under thelaminated magnetic layer structure, to thereby cancel the effect of oneof the layers. As a result, it is possible to increase the signalamplitude reproduced from the magnetic recording medium, and to alsoincrease the effective grain volume. Thermally stable written bits cantherefore be realized.

[0031] The present invention increases the thermal stability of writtenbits by exchange coupling the magnetic layer to another ferromagneticlayer with an opposite magnetization or, by a laminated ferrimagneticstructure. The ferromagnetic layer or the laminated ferrimagneticstructure is made up of exchange-decoupled grains as the magnetic layer.In other words, the present invention uses an exchange pinningferromagnetic layer or a ferrimagnetic multilayer to improve the thermalstability performance of the magnetic recording medium.

[0032]FIG. 1 is a cross sectional view showing an important part of afirst embodiment of a magnetic recording medium according to the presentinvention.

[0033] The magnetic recording medium includes a non-magnetic substrate1, a first seed layer 2, a NiP layer 3, a second seed layer 4, anunderlayer 5, a non-magnetic intermediate layer 6, a ferromagnetic layer7, a non-magnetic coupling layer 8, a magnetic layer. 9, a protectionlayer 10, and a lubricant layer 11 which are stacked in the order shownin FIG. 1.

[0034] For example, the non-magnetic substrate 1 is made of Al, Al alloyor glass. This non-magnetic substrate 1 may or may not be mechanicallytextured. The first seed layer 2 is made of Cr or Ti, for example,especially in the case where the nonmagnetic substrate 1 is made ofglass. The NiP layer 3 is preferably oxidized and may or may not bemechanically textured. The second seed layer 4 is provided to promote a(001) or a (112) texture of the underlayer 5 when using a B2 structurealloy such as NiAl and FeAl for the underlayer 5. The second seed layer4 is made of an appropriate material similar to that of the first seedlayer 2.

[0035] In a case where the magnetic recording medium is a magnetic disk,the mechanical texturing provided on the non-magnetic substrate 1 or theNiP layer 3 is made in a circumferential direction of the disk, that is,in a direction in which tracks of the disk extend.

[0036] The non-magnetic intermediate layer 6 is provided to furtherpromote epitaxy, narrow the grain distribution of the magnetic layer 9,and orient the anisotropy axes of the magnetic layer 9 along a planeparallel to the recording surface of the magnetic recording medium. Thisnon-magnetic intermediate layer 6 is made of a hcp structure alloy suchas CoCr-M, where M=B, Mo, Nb, Ta, W or alloys thereof, and has athickness in a range of 1 to 5 nm.

[0037] The ferromagnetic layer 7 is made of Co, Ni, Fe, Co-based alloy,Ni-based alloy, Fe-based alloy or the like. In other words, alloys suchas CoCrTa, CoCrPt and CoCrPt-M, where M=B, Mo, Nb, Ta, W or alloysthereof may be used for the ferromagnetic layer 7. This ferromagneticlayer 7 has a thickness in a range of 2 to 10 nm. The non-couplingmagnetic layer 8 is made of Ru, Ir, Rh, Ru-based alloy, Ir-based alloy,Rh-based alloy or the like. This non-magnetic coupling layer 8preferably has a thickness in a range of 0.4 to 0.9 nm, and preferablyon the order of approximately 0.8 nm. For this particular thicknessrange of the nonmagnetic coupling layer 8, the magnetizations of theferromagnetic layer 7 and the magnetic layer 9 are antiparallel. Theferromagnetic layer 7 and the non-magnetic coupling layer 8 form anexchange layer structure.

[0038] The magnetic layer 9 is made of Co or a Co-based alloys such asCoCrTa, CoCrPt and CoCrPt-M, where M=B, Mo, Nb, Ta, W or alloys thereof.The magnetic layer 9 has a thickness in a range of 5 to 30 nm. Ofcourse, the magnetic layer 9 is not limited to a single-layer structure,and a multilayer structure may be used for the magnetic layer 9.

[0039] The protection layer 10 is made of C, for example. In addition,the lubricant layer 11 is made of an organic lubricant, for example, foruse with a magnetic transducer such as a spin-valve head. The protectionlayer 10 and the lubricant layer 11 form a protection layer structure onthe recording surface of the magnetic recording medium.

[0040] Obviously, the layer structure under the exchange layer structureis not limited to that shown in FIG. 1. For example, the underlayer 5may be made of Cr or Cr-based alloy and formed to a thickness in a rangeof 5 to 40 nm on the substrate 1, and the exchange layer structure maybe provided on this underlayer 5.

[0041] Next, a description will be given of a second embodiment of themagnetic recording medium according to the present invention.

[0042]FIG. 2 is a cross sectional view showing an important part of thesecond embodiment of the magnetic recording medium. In FIG. 2, thoseparts which are the same as those corresponding parts in FIG. 1 aredesignated by the same reference numerals, and a description thereofwill be omitted.

[0043] In this second embodiment of the magnetic recording medium, theexchange layer structure includes two non-magnetic coupling layers 8 and8-1, and two ferromagnetic layers 7 and 7-1, which form a ferrimagneticmultilayer. This arrangement increases the effective magnetization andsignal, since the magnetizations of the two non-magnetic coupling layers8 and 8-1 cancel each other instead of a portion of the magnetic layer9. As a result, the grain volume and thermal stability of magnetizationof the magnetic layer 9 are effectively increased. More bilayerstructures made up of the pair of ferromagnetic layer and nonmagneticcoupling layer may be provided additionally to increase the effectivegrain volume, as long as the easy axis of magnetization areappropriately oriented for the subsequently provided layers.

[0044] The ferromagnetic layer 7-1 is made of a material similar to thatof ferromagnetic layer 7, and has a thickness range selected similarlyto the ferromagnetic layer 7. In addition, the nonmagnetic couplinglayer 8-1 is made of a material similar to that of the non-magneticcoupling layer 8, and has a thickness range selected similarly to thenon-magnetic coupling layer 8. Within the ferromagnetic layers 7-1 and7, the c-axes are preferably in-plane and the grain growth columnar.

[0045] In this embodiment, the magnetic anisotropy of the ferromagneticlayer 7-1 is preferably lower than that of the ferromagnetic layer 7.However, the magnetic anisotropy of the ferromagnetic layer 7-1 may bethe same as or, be higher than that of, the ferromagnetic layer 7.

[0046] Furthermore, a product of a remanent magnetization and thicknessof the ferromagnetic layer 7 may be smaller than that of theferromagnetic layer 7-1.

[0047]FIG. 3 is a diagram showing an in-plane magnetization curve of asingle CoPt layer having a thickness of 10 nm on a Si substrate. In FIG.3, the ordinate indicates the magnetization (emu), and the abscissaindicates the magnetic field (Oe). Conventional magnetic recording mediashow a behavior similar to that shown in FIG. 3.

[0048]FIG. 4 is a diagram showing an in-plane magnetization curve of twoCoPt layers separated by a Ru layer having a thickness of 0.8 nm, as inthe case of the first embodiment of the magnetic recording medium. InFIG. 4, the ordinate indicates the magnetization (Gauss), and theabscissa indicates the magnetic field (Oe). As may be seen from FIG. 4,the loop shows shifts near the magnetic field which indicate theantiparallel coupling.

[0049]FIG. 5 is a diagram showing an in-plane magnetization curve of twoCoPt layers separated by a Ru layer having a thickness of 1.4 nm. InFIG. 5, the ordinate indicates the magnetization (emu), and the abscissaindicates the magnetic field (Oe). As may be seen from FIG. 5, themagnetizations of the two CoPt layers are parallel.

[0050]FIG. 6 is a diagram showing an in-plane magnetization curve fortwo CoCrPt layers separated by a Ru having a thickness of 0.8 nm, as inthe case of the second embodiment of the magnetic recording medium. InFIG. 6, the ordinate indicates the magnetization (emu/cc), and theabscissa indicates the field (Oe). As may be seen from FIG. 6, the loopshows shifts near the field which indicate the antiparallel coupling.

[0051] From FIGS. 3 and 4, it may be seen that the antiparallel couplingcan be obtained by the provision of the exchange layer structure. Inaddition, it may be seen by comparing FIG. 0.5 with FIGS. 4 and 6, thenon-magnetic coupling layer 8 is desirably in the range of 0.4 to 0.9 nmin order to achieve the antiparallel coupling.

[0052] Therefore, according to the first and second embodiments of themagnetic recording medium, it is possible to effectively increase theapparent grain volume of the magnetic layer by the exchange couplingprovided between the magnetic layer and the ferromagnetic layer via thenon-magnetic coupling layer, without sacrificing the resolution. Inother words, the apparent thickness of the magnetic layer is increasedwith regard to the grain volume of the magnetic layer so that athermally stable medium can be obtained, and in addition, the actualthickness of the magnetic layer is not increased so that the resolutionremains unaffected by the increased “apparent thickness” of the magneticlayer. As a result, it is possible to obtain a magnetic recording mediumwith reduced medium noise and thermally stable performance.

[0053] Next, a description will be given of an embodiment of a magneticstorage apparatus according to the present invention, by referring toFIGS. 7 and 8. FIG. 7 is a cross sectional view showing an importantpart of this embodiment of the magnetic storage apparatus, and FIG. 8 isa plan view showing the important part of this embodiment of themagnetic storage apparatus.

[0054] As shown in FIGS. 7 and 8, the magnetic storage apparatusgenerally includes a housing 13. A motor 14, a hub 15, a plurality ofmagnetic recording media 16, a plurality of recording and reproducingheads 17, a plurality of suspensions 18, a plurality of arms 19, and anactuator unit 20 are provided within the housing 13. The magneticrecording media 16 are mounted on the hub 15 which is rotated by themotor 14. The recording and reproducing head 17 is made up of areproducing head such as a MR or GMR head, and a recording head such asan inductive head. Each recording and reproducing head 17 is mounted onthe tip end of a corresponding arm 19 via the suspension 18. The arms 19are moved by the actuator unit 20. The basic construction of thismagnetic storage apparatus is known, and a detailed description thereofwill be omitted in this specification.

[0055] This embodiment of the magnetic storage apparatus ischaracterized by the magnetic recording media 16. Each magneticrecording medium 16 has the structure of the first or second embodimentof the magnetic recording medium described above in conjunction withFIGS. 1 and 2. Of course, the number of magnetic recording media 16 isnot limited to three, and only one, two or four or more magneticrecording media 16 may be provided.

[0056] The basic construction of the magnetic storage unit is notlimited to that shown in FIGS. 7 and 8. In addition, the magneticrecording medium used in the present invention is not limited to amagnetic disk.

[0057] Therefore, according to the present invention, it is possible toprovide a magnetic recording medium and a magnetic storage apparatus,which can improve the thermal stability of written bits and reduce themedium noise, so as to enable reliable high-density recording withoutintroducing adverse effects on the performance of the magnetic recordingmedium.

[0058] Further, the present invention is not limited to theseembodiments, but various variations and modifications may be madewithout departing from the scope of the present invention.

What is claimed is:
 1. A magnetic recording medium comprising: at leastone exchange layer structure; and a magnetic layer formed on saidexchange layer structure, said exchange layer structure comprising: aferromagnetic layer; and a non-magnetic coupling layer provided on saidferromagnetic layer and under said magnetic layer, said ferromagneticlayer and said magnetic layer having antiparallel magnetizations.
 2. Themagnetic recording medium as claimed in claim 1, wherein saidferromagnetic layer is made of a material selected from a groupconsisting of Co, Ni, Fe, Ni-based alloys, Fe-based alloys, and Co-basedalloys including CoCrTa, CoCrPt and CoCrPt-M, where M=B, Mo, Nb, Ta, Wor alloys thereof.
 3. The magnetic recording medium as claimed in claim1, wherein said ferromagnetic layer has a thickness in a range of 2 to10 nm.
 4. The magnetic recording medium as claimed in claim 1, whereinsaid non-magnetic coupling layer is made of a material selected from agroup of Ru, Rh, Ir, Ru-based alloys, Rh-based alloys, and Ir-basedalloys.
 5. The magnetic recording medium as claimed in claim 1, whereinsaid non-magnetic coupling layer has a thickness in a range of 0.4 to0.9 nm.
 6. The magnetic recording medium as claimed in claim 1, whereinsaid magnetic layer is made of a material selected from a group of Co,and Co-based alloys including CoCrTa, CoCrPt and CoCrPtM, where M=B, Mo,Nb, Ta, W or alloys thereof.
 7. The magnetic recording medium as claimedin claim 1, which further comprises: a substrate; and an underlayerprovided above said substrate, said exchange layer structure beingprovided above said underlayer.
 8. The magnetic recording medium asclaimed in claim 7, which further comprises: a non-magnetic intermediatelayer interposed between said underlayer and said exchange layerstructure, said non-magnetic intermediate layer having a hcp structurealloy selected from a group of CoCr-M, where M=B, Mo, Nb, Ta, W oralloys thereof, and having a thickness in a range of 1 to 5 nm.
 9. Themagnetic recording medium as claimed in claim 8, which furthercomprises: a NiP layer interposed between said substrate and saidunderlayer, said NiP layer being mechanically textured or oxidized. 10.The magnetic recording medium as claimed in claim 7, wherein saidunderlayer is made of a B2 structure alloy selected from a group of NiAland FeAl.
 11. The magnetic recording medium as claimed in claim 1, whichcomprises at least a first exchange layer structure and a secondexchange layer structure interposed between said first exchange layerstructure and said magnetic layer, wherein a ferromagnetic layer of saidsecond exchange layer structure has a magnetic anisotropy lower thanthat of a ferromagnetic layer of said first exchange layer structure,and magnetizations of the ferromagnetic layers of said first and secondexchange layer structures are antiparallel.
 12. The magnetic recordingmedium as claimed in claim 1, which comprises at least a first exchangelayer structure and a second exchange layer structure interposed betweensaid first exchange layer structure and said magnetic layer, wherein aproduct of a remanent magnetization and thickness of a ferromagneticlayer of said second exchange layer structure is smaller than that of aferromagnetic layer of said first exchange layer structure, andmagnetizations of the ferromagnetic layers of said first and secondexchange layer structures are antiparallel.
 13. A magnetic storageapparatus comprising: at least one magnetic recording medium includingat least one exchange layer structure, and a magnetic layer formed onsaid exchange layer structure; and at least one head recordinginformation on and/or reproducing information from the recording medium,said exchange layer structure comprising: a ferromagnetic layer; and anon-magnetic coupling layer provided on said ferromagnetic layer andunder said magnetic layer, said ferromagnetic layer and said magneticlayer having antiparallel magnetizations.
 14. The magnetic storageapparatus as claimed in claim 13, wherein said ferromagnetic layer ismade of a material selected from a group consisting of Co, Ni, Fe,Ni-based alloys, Fe-based alloys, and Co-based alloys including CoCrTa,CoCrPt and CoCrPt-M, where M=B, Mo, Nb, Ta, W or alloys thereof.
 15. Themagnetic storage apparatus as claimed in claim 13, wherein saidferromagnetic layer has a thickness in a range of 2 to 10 nm.
 16. Themagnetic storage apparatus as claimed in claim 13, wherein saidnon-magnetic coupling layer is made of a material selected from a groupof Ru, Rh, Ir, Ru-based alloys, Rh-based alloys, and Ir-based alloys.17. The magnetic storage apparatus as claimed in claim 13, wherein saidnon-magnetic coupling layer has a thickness in a range of 0.4 to 0.9 nm.18. The magnetic storage apparatus as claimed in claim 13, wherein saidmagnetic layer is made of a material selected from a group of Co, andCo-based alloys including CoCrTa, CoCrPt and CoCrPtM, where M=B, Mo, Nb,Ta, W or alloys thereof.